Biomedical subjects

X Yu

Publications and source records attributed to X Yu.

At least 19 recordsLinked to original sources

PubMed2002

PPAR alpha is necessary for the lipopenic action of hyperleptinemia on white adipose and liver tissue.

Adenovirus-induced hyperleptinemia causes rapid disappearance of body fat in normal rats, presumably by up-regulating fatty acid oxidation within white adipocytes. To determine the role of peroxisomal proliferation-activated receptor (PPAR)alpha expression, which was increased during the rapid loss of fat, we infused adenovirus-leptin into PPAR alpha(-/-) and PPAR alpha(+/+) mice. Despite similar degrees of hyperleptinemia and reduction in food intake, epididymal fat pad weight declined 55% in wild-type but only 6% in PPAR alpha(-/-) mice; liver triacylglycerol fell 39% in the wild-type group but was unchanged in PPAR(-/-) mice. Carnitine palmitoyl transferase-1 mRNA rose 52% in the wild-type mice but did not increase in PPAR alpha(-/-) mice. PPAR gamma coactivator-1 alpha rose 3-fold in the fat and 46% in the liver of wild-type mice but was unchanged in PPAR alpha(-/-) mice. Although AMP-activated protein kinase could not be implicated in the lipopenic actions of hyperleptinemia, acetyl CoA carboxylase protein was reduced in the liver of wild-type but not in PPAR alpha(-/-) mice. Thus, in PPAR alpha(-/-) mice, up-regulation of carnitine palmitoyl transferase-1 mRNA in fat, down-regulation of acetyl CoA carboxylase in liver, and up-regulation of PPAR gamma coactivator-1 alpha mRNA in both tissues are abolished, as is the reduction in their triacylglycerol content.

AMP-Activated Protein Kinases↗

PubMed2002

Analysis of glucose and lactate in dialysate from hypothalamus of rats after exhausting swimming using microdialysis.

A microbore flow injection analysis-immobilized enzyme reactor-electrochemical detection (FIA-IMER-ECD) system for glucose and lactate detection was built up. The assays were precise, sensitive and practicable for determination of glucose and lactate levels in hypothalamic dialysate. The method had been used to detect the dynamic changes of glucose and lactate levels during rat exhausting swimming and recovery. The data showed that after exhausting swimming, the concentration of glucose in hypothalamic dialysate that reflected the concentration in the hypothalamic extracellular fluid decreased. The level fell to its nadir at day 1 after the exercise and then went back to the basal level at day 3 after the swimming. However, lactate levels increased to a maximum at day 3 and went back to the basal level at day 5 after the swimming.

Animals↗

PubMed2001

Reversal of GSTP1 CpG island hypermethylation and reactivation of pi-class glutathione S-transferase (GSTP1) expression in human prostate cancer cells by treatment with procainamide.

Among the many somatic genome alterations present in cancer cells, changes in DNA methylation may represent reversible "epigenetic" lesions, rather than irreversible "genetic" alterations. Cancer cell DNA is typically characterized by increases in the methylation of CpG dinucleotides clustered into CpG islands, near the transcriptional regulatory regions of critical genes, and by an overall reduction in CpG dinucleotide methylation. The transcriptional "silencing" of gene expression associated with such CpG island DNA hypermethylation presents an attractive therapeutic target: restoration of "silenced" gene expression may be possible via therapeutic reversal of CpG island hypermethylation. 5-Aza-cytidine (5-aza-C) and 5-aza-deoxycytidine (5-aza-dC), nucleoside analogue inhibitors of DNA methyltransferases, have been widely used in attempts to reverse abnormal DNA hypermethylation in cancer cells and restore "silenced" gene expression. However, clinical utility of the nucleoside analogue DNA methyltransferase inhibitors has been limited somewhat by myelosuppression and other side effects. Many of these side effects are characteristic of nucleoside analogues that are not DNA methyltransferase inhibitors, offering the possibility that nonnucleoside analogue DNA methyltransferase inhibitors might not possess such side effects. Human prostate cancer (PCA) cells characteristically contain hypermethylated CpG island sequences encompassing the transcriptional regulatory region of GSTP1, the gene encoding the pi-class glutathione S-transferase (GSTP1), and fail to express GSTP1 as a consequence of transcriptional "silencing." Inactivation of GSTP1 by CpG island hypermethylation, the most common somatic genome alteration yet reported for human PCAs, occurs early during human prostatic carcinogenesis and results in a loss of GSTP1 "caretaker" function, leaving prostate cells with inadequate defenses against oxidant and electrophile carcinogens. We report here that the drug procainamide, a nonnucleoside inhibitor of DNA methyltransferases, reversed GSTP1 CpG island hypermethylation and restored GSTP1 expression in LNCaP human PCA cells propagated in vitro or in vivo as xenograft tumors in athymic nude mice.

Animals↗

PubMed2001

CD9 amino acids critical for upregulation of diphtheria toxin binding.

CD9 associates with a diphtheria toxin receptor (DTR) that is identical to the membrane-anchored form of heparin-binding EGF-like growth factor. We determined the region of CD9 important for upregulation activity. Human and monkey CD9 upregulates DT binding activity of DTR, while mouse CD9 has no upregulation activity. Transfection of chimeric constructs comprising monkey and mouse CD9s showed that the human sequence between Ala156 and Asp183 is essential for the upregulation activity. Studies of mutants, replacing a single amino acid within the region between Ala156 and Asp183 of monkey CD9 with the corresponding amino acid residue in mouse CD9, revealed that substitution of Gly158 is critical for the reduction of the upregulation activity and secondly for the substitution of Val159 and Thr175. These three amino acid residues were deduced to be located on the head domain of the second extracellular loop, suggesting that interactions of CD9 with DTR or DT at the domain containing these three amino acids were important for the upregulation of DT binding.

Amino Acid Sequence↗

PubMed2001

Archaeal RadA protein binds DNA as both helical filaments and octameric rings.

The Escherichia coli RecA protein has been a model for understanding homologous eukaryotic recombination proteins such as Rad51. The active form of both RecA and Rad51 appear to be helical filaments polymerized on DNA, in which an unusual helical structure is induced in the DNA. Surprisingly, the human meiosis-specific homolog of RecA, Dmc1, has thus far only been observed to bind DNA as an octameric ring. Sequence analysis and biochemical studies have shown that archaeal RadA proteins are more closely related to Rad51 and Dmc1 than the bacterial RecA proteins. We find that the Sulfolobus solfataricus RadA protein binds DNA in the absence of nucleotide cofactor as an octameric ring and in the presence of ATP as a helical filament. Since it is likely that RadA is closely related to a common ancestral protein of both Rad51 and Dmc1, the two DNA-binding forms of RadA may provide insight into the divergence that has taken place between Rad51 and Dmc1.

Adenosine Triphosphatases↗

PubMed2001

Phylogenetic comparison of classical swine fever virus in China.

An N-terminal fragment of the E2 gene of classical swine fever (CSF) virus encoding major immunogenic sites was amplified by RT-PCR directly from 110 clinical specimens representing 109 epizootic sites during the last decade in China. Phylogenetic relationships between these viruses as well as 20 reference strains were determined by comparison of their nucleotide sequences. A phylogenetic tree showed that 103 of the 110 field viruses (93.6%) were clustered within group 2 and subdivided into three subgroups, while the remaining seven viruses (6.4%), along with two Chinese reference strains, Shimen and HCLV (attenuated vaccine strain), were clustered into subgroup 1.1 within group 1. However, none of the Chinese CSF viruses were members of subgroup 1.2 (represented by reference strain Brescia). This is the first report on the distribution of CSF virus genotypes in China. Results indicated that CSF viruses predominating in recent epizootics within China are genetically divergent from the reference strain Shimen and the vaccine strain HCLV.

Animals↗

PubMed2001

Relation of gene expression phenotype to immunoglobulin mutation genotype in B cell chronic lymphocytic leukemia.

The most common human leukemia is B cell chronic lymphocytic leukemia (CLL), a malignancy of mature B cells with a characteristic clinical presentation but a variable clinical course. The rearranged immunoglobulin (Ig) genes of CLL cells may be either germ-line in sequence or somatically mutated. Lack of Ig mutations defined a distinctly worse prognostic group of CLL patients raising the possibility that CLL comprises two distinct diseases. Using genomic-scale gene expression profiling, we show that CLL is characterized by a common gene expression "signature," irrespective of Ig mutational status, suggesting that CLL cases share a common mechanism of transformation and/or cell of origin. Nonetheless, the expression of hundreds of other genes correlated with the Ig mutational status, including many genes that are modulated in expression during mitogenic B cell receptor signaling. These genes were used to build a CLL subtype predictor that may help in the clinical classification of patients with this disease.

Gene Expression↗

PubMed2001

Asthma is associated with weight gain in females but not males, independent of physical activity.

We tested whether asthma diagnosis is associated with weight gain and physical activity in 4,547 18 to 30-yr-old African American and white men and women, followed prospectively for up to 10 yr. Baseline asthma was most frequent in African American men. Incident asthma was more frequent in women. Incident asthma was associated with highest and lowest baseline and change in body mass index (BMI), in a J-shaped curve, after adjustment for other factors. When stratified by sex, this association was seen only in females. Subjects on average decreased physical activity and gained weight over time, but there was no significant difference in asthma prevalence by physical activity at baseline or asthma incidence by change in physical activity. Cigarette smoking in females was significantly associated with asthma incidence, but serum cotinine level at baseline among nonsmokers (reflecting environmental tobacco smoke [ETS] exposure) was not significantly associated with asthma. We conclude that gain in BMI predisposes to new asthma diagnosis in female young adults, but decreased physical activity does not explain the association of weight gain with asthma.

Adolescent↗

PubMed2001

Dorsal root ganglia neurite extension is inhibited by mechanical and chondroitin sulfate-rich interfaces.

Glial scar formation plays a critical role in the regenerative failure in the central nervous system of adult mammals through the formation of mechanical or biochemical barriers as a result of its molecular composition. In this study, we report an in vitro model to study growth-cone behavior at controlled 3D interfaces using layered agarose hydrogels. The behavior of growth cones from embryonic day 9 (E9) chick dorsal root ganglia (DRGs) at interfaces that were mismatched in terms of their elasticity or chondroitin sulfate content was quantitatively determined. A mechanical barrier formed by the elasticity mismatch of layered agarose gels greatly influenced the ability of neurites from E9 DRGs to cross the 3D interface. To form chondroitin sulfate-rich interfaces, chondroitin sulfate B was covalently coupled to agarose hydrogel. Compared with unmodified agarose gels, the presence of CS-B-modified agarose gels at the interface significantly inhibited E9 DRGs neurites. After treatment of CS-B-modified agarose gels with chondroitinase ABC, the inhibitory effects of CS-B at the interface were significantly decreased. The effect of doping CS-B gels with laminin 1 (LN-1)-coupled agarose gels was investigated as a potential strategy to overcome inhibitory interfaces. When CS-B agarose gels were doped with LN-1-coupled agarose gels, DRG neurite's ability to cross 3D interfaces was significantly enhanced compared with that of non-LN-1-containing interfaces presenting equivalent CS-B. Our in vitro model may be used to study the influence of individual components of glial scar on inhibition as well as to design strategies to overcome this inhibition.

Animals↗

PubMed2001

Comparison of bacteriophage T4 UvsX and human Rad51 filaments suggests that RecA-like polymers may have evolved independently.

The UvsX protein from bacteriophage T4 is a member of the RecA/Rad51/RadA family of recombinases active in homologous genetic recombination. Like RecA, Rad51 and RadA, UvsX forms helical filaments on DNA. We have used electron microscopy and a novel method for image analysis of helical filaments to show that UvsX-DNA filaments exist in two different conformations: an ADP state and an ATP state. As with RecA protein, these two states have a large difference in pitch. Remarkably, even though UvsX is only weakly homologous to RecA, both UvsX filament states are more similar to the RecA crystal structure than are RecA-DNA filaments. We use this similarity to fit the RecA crystal structure into the UvsX filament, and show that two of the three previously described blocks of similarity between UvsX and RecA are involved in the subunit-subunit interface in both the UvsX filament and the RecA crystal filament. Conversely, we show that human Rad51-DNA filaments have a different subunit-subunit interface than is present in the RecA crystal, and this interface involves two blocks of sequence similarity between Rad51 and RecA that do not overlap with those found between UvsX and RecA. This suggests that helical filaments in the RecA/Rad51/RadA family may have arisen from convergent evolution, with a conserved core structure that has assembled into multimeric filaments in a number of different ways.

Adenosine Diphosphate↗

PubMed2001

In vitro targeted killing of prostate tumor cells by a synthetic amoebapore helix 3 peptide modified with two gamma-linked glutamate residues at the COOH terminus.

Prostate-specific membrane antigen (PSMA) is a trans-membrane protein specifically expressed in LNCaP cells, malignant human prostate tissues, and the surrounding neovasculature. PSMA is a unique exopeptidase with reactivity toward poly-gamma-glutamated folates. It can sequentially remove the poly-gamma-glutamyl termini. To target prostate tumor cells, a novel procytolytic peptide was designed with a backbone consisting of an amoebapore H3 domain modified by two gamma-linked glutamate residues at the epsilon-amino group of the COOH-terminal lysine residue. The strategy behind the design of this prolytic peptide was to inactivate the lytic amoebapore H3 peptide by replacing its functionally important COOH-terminal positive charge with negatively charged groups, which in turn might be selectively removed by the PSMA exopeptidase. This peptide exhibited little cytolytic activity toward PSMA-negative cells, such as PC-3 cells. On the other hand, this peptide exhibited strong cytolytic activity toward PSMA-positive LNCaP cells in a concentration-dependent manner. The carboxypeptidase inhibitor 4,4'-phosphonicobis (butane-1,3-dicarboxylic acid) can inhibit this activity. Moreover, this peptide also exhibited cytolytic activity toward PSMA cDNA-transfected PC-3 cells.

Amino Acid Sequence↗

PubMed2001

The primase active site is on the outside of the hexameric bacteriophage T7 gene 4 helicase-primase ring.

Gene 4 of bacteriophage T7 encodes a protein (gp4) that can translocate along single-stranded DNA, couple the unwinding of duplex DNA with the hydrolysis of dTTP, and catalyze the synthesis of short RNA oligoribonucleotides for use as primers by T7 DNA polymerase. Electron microscopic studies have shown that gp4 forms hexameric rings, and X-ray crystal structures of the gp4 helicase domain and of the highly homologous RNA polymerase domain of Escherichia coli DnaG have been determined. Earlier biochemical studies have shown that when single-stranded DNA is bound to the hexameric ring, the primase domain remains accessible to free DNA. Given these results, a model was suggested in which the primase active site in the gp4 hexamer is located on the outside of the hexameric ring. We have used electron microscopy and single-particle image analysis to examine T7 gp4, and have determined that the primase active site is located on the outside of the hexameric ring, and therefore provide direct structural support for this model.

Amino Acid Sequence↗

PubMed2001

Domain structure and dynamics in the helical filaments formed by RecA and Rad51 on DNA.

Both the bacterial RecA protein and the eukaryotic Rad51 protein form helical nucleoprotein filaments on DNA that catalyze strand transfer between two homologous DNA molecules. However, only the ATP-binding cores of these proteins have been conserved, and this same core is also found within helicases and the F1-ATPase. The C-terminal domain of the RecA protein forms lobes within the helical RecA filament. However, the Rad51 proteins do not have the C-terminal domain found in RecA, but have an N-terminal extension that is absent in the RecA protein. Both the RecA C-terminal domain and the Rad51 N-terminal domain bind DNA. We have used electron microscopy to show that the lobes of the yeast and human Rad51 filaments appear to be formed by N-terminal domains. These lobes are conformationally flexible in both RecA and Rad51. Within RecA filaments, the change between the "active" and "inactive" states appears to mainly involve a large movement of the C-terminal lobe. The N-terminal domain of Rad51 and the C-terminal domain of RecA may have arisen from convergent evolution to play similar roles in the filaments.

DNA↗

PubMed2001

The human erythropoietin receptor gene rescues erythropoiesis and developmental defects in the erythropoietin receptor null mouse.

Erythropoietin and its receptor are required for definitive erythropoiesis and maturation of erythroid progenitor cells. Mice lacking the erythropoietin receptor exhibit severe anemia and die at about embryonic day 13.5. This phenotype can be rescued by the human erythropoietin receptor transgene. Animals expressing only the human erythropoietin receptor survived through adulthood with normal hematologic parameters and appeared to respond appropriately to induced anemic stress. In addition to restoration of erythropoiesis during development, the cardiac defect associated with embryos lacking the erythropoietin receptor was corrected and the increased apoptosis in fetal liver, heart, and brain in the erythropoietin receptor null phenotype was markedly reduced. These studies indicate that no species barrier exists between mouse and human erythropoietin receptor and that the human erythropoietin receptor transgene is able to provide specific expression in hematopoietic and other selected tissues to rescue erythropoiesis and other organ defects observed in the erythropoietin receptor null mouse.

Anemia↗

PubMed2001

Expression of a micro-protein.

The smallest known open reading frame encodes the ribosomal protein L41, which in yeast is composed of only 24 amino acids, 17 of which are arginine or lysine. Because of the unique problems that might attend the translation of such a short open reading frame, we have investigated the properties and the translation of the mRNAs encoding L41. In Saccharomyces cerevisiae L41 is encoded by two linked genes, RPL41A and RPL41B. These genes give rise to mRNAs that have short 5' leaders of 18 and 22 nucleotides and rather long 3' leaders of 203 and 210 nucleotides not including their poly(A) tails. The mRNAs are translated exclusively on monosomes, suggesting that ribosomes do not remain attached to the mRNA after termination of translation. Calculations based on the abundance of ribosomes and of L41 mRNA indicate that the entire translation event, from initiation through termination, must occur in approximately 2 s. Termination of translation after only 25 codons does not subject the mRNAs encoding L41 to nonsense-mediated decay. Surprisingly, despite the L41 ribosomal protein being conserved from the archaea through the mammalia, S. cerevisiae can grow relatively normally after deletion of both RPL41A and RPL41B.

3' Untranslated Regions↗

PubMed2001

Involvement of Bcl-2 family genes and Fas signaling system in primary and secondary male germ cell apoptosis induced by 2-bromopropane in rat.

Epidemiological surveys and animal experimental studies suggest that exposure to 2-bromopropane (2-BP) could result in reproductive and hematopoietic disorders. The objectives of this study were to investigate the role of apoptosis in 2-BP-induced testicular toxicity and whether this process involves Bcl-2 family genes and the Fas signaling system. Rats were injected percutaneously with 1350 mg/kg 2-BP for 1 to 5 days and then were euthanized at 6 or 12 h after one dose, 6 h after two, three, or five doses, and 2 or 9 days after the final treatment. Light and electron microscopic analyses, TUNEL staining of DNA fragments, agarose gel electrophoresis of low-molecular-weight DNA, and Western blotting analysis of Bcl-2 family proteins and Fas receptor and ligand were conducted. Two-day treatment resulted in selective degeneration of spermatogonia with marked nuclear chromatin condensation. DNA ladder formation on the agarose gel further validated the findings of TUNEL-stained apoptotic cells. The percentage of apoptotic-positive tubules and apoptotic cell index increased time dependently. 2-BP treatment resulted in two distinct morphological changes: an immediate effect on spermatogonia and secondary apoptosis of spermatocytes 9 days after treatment. Downregulation of Bcl-2 after the first or second injection of 2-BP and upregulation of Bax after the first treatment contributed to the initiation of primary apoptosis of spermatogonia. Expression of FasL was inhibited while expression of Fas increased after the 2-BP treatment and remained at levels about two times of the control. However, it increased about sixfold of the control by day 9 after final injection, which contributed to the induction of secondary apoptosis of spermatocytes. Our results indicate that 2-BP resulted in apoptotic death of testicular germ cells and that this process involves the Bcl-2 family genes and the Fas signaling system.

Animals↗

PubMed2001

Advances in transplantation tolerance.

Immunosuppressive drugs developed in the past two decades have improved the short-term survival of organ allografts, but tolerance has not been achieved and almost all transplant recipients continue to require drugs throughout life. Graft rejection arises from the cognate interaction of T cells with antigen-presenting cells, the recognition of alloantigen through the T-cell receptor, and the delivery of accessory stimulation signals. Once activated by the specific antigen, replicating T cells die if they are re-exposed to the same antigen. Since depletion of antigen-activated T cells is one critical mechanism of transplantation tolerance, drugs such as ciclosporin that interfere with activation-induced T-cell death could inhibit tolerance, whereas drugs such as mycophenolate mofetil, that induce the death of activated T cells, could facilitate tolerance. Other tolerance mechanisms depend on inactivation rather than elimination of allograft reactive T cells. When antigen recognition occurs without costimulation through the CD28 and CD154 accessory receptors, or in absence of cell division, T cells become unresponsive. Thus, inhibitors of CD28 and CD154, and inhibition of T-cell division by rapamycin promotes transplantation tolerance.

CD28 Antigens↗

PubMed2001

Crystallization and preliminary X-ray crystallographic studies of wild-type human ornithine transcarbamylase and two naturally occurring mutants at position 277.

Wild-type human ornithine transcarbamylase (OTCase) and two mutants (R277Q and R277W) that cause 'late-onset' hyperammonemia were crystallized and a preliminary structure determination was carried out. The unliganded wild-type enzyme crystallizes in the cubic space group I23, with unit-cell parameters a = b = c = 203.4 A. R277Q crystallizes in two crystal forms under the same crystallization conditions. One crystal form is isomorphous to that of unliganded wild-type crystals, with unit-cell parameters a = b = c = 202.2 A. The second form also belongs to a cubic space group, P4(3)32, but has unit-cell parameters a = b = c = 139.8 A. R277W crystals are isomorphous to the second crystal form of R277Q, with unit-cell parameters a = b = c = 138.7 A. None of these crystal forms is isomorphous to other crystal forms of OTCase that have been studied. The structures in both crystal forms have been solved using molecular replacement. In the first crystal form there are two monomers in the asymmetric unit, corresponding to a solvent content of 75%. Because of its high molecular and crystal symmetry and the presence of non-crystallographic symmetry, this structure could not be solved with AMoRe or X-PLOR, but was solved successfully with COMO. There is only one monomer in the asymmetric unit in the second crystal form, corresponding to a solvent content of 62%. This structure was successfully solved with AMoRe.

Crystallization↗